Under Garage Home Theater Build

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ecut1
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Re: Under Garage Home Theater Build

#16 Post by ecut1 »

I have thought about the option of leaving the ceiling and screen wall without sheetrock. They'd simply stay as netted cellulose and get covered with decorative fabric tiles (ceiling) and a fabric covered baffle wall (screen wall). 6 inches of cellulose seems to absorb sound fairly well.

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#17 Post by Bill Fitzmaurice »

I think that would over-damp the room. You don't want to create an anechoic chamber, or even close to it.

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Re: Under Garage Home Theater Build

#18 Post by ecut1 »

Maybe just leave the baffle wall in raw cellulose then? I could cover it with black fabric to absorb any light that gets through the screen. It seems like the general idea is to have a lot of sound dampening behind the screen on the baffle wall. I'd mount my TLAH's and curved SLA to that wall with the screen wall about 10" away - speakers firing through the screen. Here's a pic of the room looking towards the wall where the screen will be. How about dolby atmos? Worth all the trouble of 4 ceiling speakers??
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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#19 Post by Bill Fitzmaurice »

IMO Atmos=Dolby jumped the shark.

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Re: Under Garage Home Theater Build

#20 Post by jimbo7 »

I've always wondered why builders don't utilize the space under a garage when building foundations. I know weight is the main factor, but that'd be a selling point for me. With a 3 car garage, that would make my basement huge. I wouldn't build a bedroom under it, but more storage or a hi-fi room would be awesome.
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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#21 Post by Bill Fitzmaurice »

It would be expensive, requiring either steel girders with a poured floor or steel reinforced pre-cast.

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Re: Under Garage Home Theater Build

#22 Post by ecut1 »

It added around 20k to our house build. That's the hollow core, extra wall height, and extra floor flat work. It ends up right around $20 or so per square foot. It's fairly inexpensive but for sure not something a builder would add to a spec house.

As far as front speaker placement... The seating area will be around 14 feet from the screen. I'm going with a 110" screen which is 8 feet wide. The center channel will be placed behind the screen at about ear level when seated (acoustically transparent screen material). Should the left and right also be placed behind the screen? (basically 8 feet apart) Or should I put openings in the outer wall and get them separated further? The room is 13.5 feet wide so I can end up with the whole triangle idea. But I've also read you don't want the left and right too far away from the screen to create too wide of a sound stage.

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Re: Under Garage Home Theater Build

#23 Post by Bill Fitzmaurice »

If you haven't built the curved SLA yet you should reconsider. With behind the screen placement you can use a vertical TLAH. The screen will affect the sound, mainly in the highs, so if the center is behind the screen the L/R should be as well. At 14 feet from the screen an 8 foot L/R separation is adequate. That's what I have.

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Re: Under Garage Home Theater Build

#24 Post by ecut1 »

Curved SLA is already built. I guess I could rebuild it in a TLAH cabinet. I used all the same speakers for the three. I might have extra tweeters. That would allow the distance between the baffle wall and the screen wall to be more shallow. My curved SLA is 14" deep at the ends! Crossovers would be different though, right? Maybe not worth it...

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Re: Under Garage Home Theater Build

#25 Post by Bill Fitzmaurice »

Try it, if it's good then no worries.

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Rick Lee
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Re: Under Garage Home Theater Build

#26 Post by Rick Lee »

Are you building a room within a room? Without looking too carefully that's what it looks like. With all the concrete it's a little bit of overkill but if that's really what you're going for I'm curious what you're doing with the door and HVAC system. It's a whole nother world if you're trying to minimize sound leakage.
I will disagree with Bill on this: You do want controlled absorption for even frequency response. The concrete WILL keep the audio energy in the room so the key is to try to even out the response and reverb at the listening positions. Since this is a purpose built HT room having a controlled sound with a low RT60 is desirable. It's not a room where you're going to be sitting around talking.
There's all kinds of info out there about how to do this. I'm in the middle of building a studio and it's mind boggling all the resources available. It doesn't have to be expensive since your room has "good bones". It is a small room so absorption is your friend. If you are going for room in a room I would put drywall on the outside (toward the concrete) and use rockwool insulation in the studs so you could cover it for absorption/diffraction, etc. Things like some bass trapping in the corners, mass loaded vinyl, hemholtz resonators, etc. Mass loaded vinyl can get a little expensive but the other treatments can be cheap. For instance you can buy 2" thick 2'x4' rigid insulation for about $3
There's several free or almost free software to help measure your room, such as REW. There are many forums on treating your room. If you want the technical side of things go to the music studio forums. Some of them get snobbish but just reading through them will give you a good grasp on details that can make the room sound great.
And yes, absolutely use a TLAH for your center channel to match L & R. The screen side could be a dead wall but you may want to consider soffit mounting your speakers. I would keep the ceiling dead because it will give the audio illusion of height.
It's rare to see a room that's all concrete. It's like a blank canvas with all kinds of possibilities!!
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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#27 Post by Bill Fitzmaurice »

Rick Lee wrote: Thu Feb 28, 2019 12:17 am The concrete WILL keep the audio energy in the room
No more than drywall. Where concrete differs from drywall or other materials is how much sound is radiated on the other side. This goes to a basic property of sound waves: they do not pass through walls. Their energy is imparted to the wall, and if that energy is sufficient to cause the wall to vibrate on its opposite side that opposite side will then radiate sound waves. If the mass of the wall is too great for the imparted energy to cause it to vibrate sound won't be radiated on the other side. It's a logical assumption that the reason concrete walls don't radiate sound on the other side as well as drywall or any lighter construction is because the sound waves are better contained in the room by concrete, but this is another example of where logic is incorrect. The proof of this is to measure the reflected sound level off walls made of various constructions. I've done so, and it's quite uniform. I've even seen it said that window glass acts as a bass trap of sorts, because it allows bass to pass through so easily. It doesn't. I measured the reflected sound level off glass compared to an inch of drywall, it was exactly the same. Bass is radiated on the opposite side of glass far more than a typical wall, because glass is so easily vibrated.

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Rick Lee
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Re: Under Garage Home Theater Build

#28 Post by Rick Lee »

Correct. Just trying to keep things simple for the OP. He currently has a single leaf structure that has a lot of mass. Because of the mass only the lowest frequencies will have enough energy to cause the floor, walls and ceilings to resonate and thus radiate sound to the other side. The simplest way to express this is to say that the concrete will keep the audio energy in the room.

Though I didn't say it directly my concern, especially after seeing the picture with the stud walls is for the OP to have a "balanced" system. In other words, he has a "Cadillac" for a basic room and it would only be fair to hold the rest of the HT system to the same standard. It doesn't need to be expensive, but just take care with the rest of the install.

By installing the stud wall and ceiling and making it a two leaf system he's implying that sound isolation is very important to him. Thus my question about the door and the HVAC system. I visited a studio once that an older man built after his wife passed on. He had built a new building with sand filled cinder block walls with a tracking room and separate control room. The doors were heavy and well sealed. He had sound panels up. He had double walls between rooms with a heavy double paned window between the two rooms. And then I noticed..., underneath the console desk was a neatly trimmed, completely open 6" square hole where he had passed an audio snake between rooms. All that work for sound isolation and it was ruined because of that little hole. But, he was happy and I didn't say anything. What he really wanted was to have vintage instruments and amps and a room that looked like a studio and a place for friends to come hang out. Pretty cool really with thousands of dollars worth of stuff. He had an amp (with the price tag still on it) that Paul McCartney had played on. But still. If the hole wasn't there he would have had much better isolation.

So all I'm trying to say is that you, the OP, have the good basics of a room and instead of making it mediocre sounding put some effort in to make it sound worthy. I'll be glad to give recommendations. If the stud wall is merely there to hang electrical outlets and put in some insulation that's fine. If you are in fact making a double leaf system that's fine also but you're moving into another league of balancing things. Which is it? Are you wanting it to be done quickly and be "okay" (nothing wrong with that) or are you wanting it to be deeply thought out and super special?
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ecut1
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Re: Under Garage Home Theater Build

#29 Post by ecut1 »

The room is a 6 sided concrete box. Above it is what appears to be a standard garage, cars parked, etc. Then I have framed a box within the concrete box. Finished dimensions are around 13.5 x 23.5. The framed 2x4 walls sit between and inch to two inches away from the concrete. I would like to make it as nice as possible but it's mostly DIY. I’ll probably hire sheetrock and carpet. I’m a trim carpenter.
I have a set of TLAH's, a curved SLA, and dual table tubas from builds several years ago in a previous house.

viewtopic.php?f=30&t=20769
viewtopic.php?f=30&t=20703
viewtopic.php?f=31&t=21203&p=236585#p236585

I’m a bit of a bass addict. I might build a THT to add to the mix later. I know that’s overkill.

As far and penetrations into the room… I had to cut one eight inch hole in one concrete wall to pass wiring through and plumbing (for the garage drain). I plan to fill that completely with foam insulation before insulating the 2x4 walls. The door is a solid core wood door in an exterior frame with seals on all 4 sides. It will probably be the weak link for sound getting out of the room (I’m thinking about some sort of tuck and roll upholstery for the inside of the door). No HVAC in that room. I've wired for cove heaters in the winter and we don't really need AC below grade in Idaho - basements stay fairly cool in the summer.
So yeah, the room is still pretty much a blank canvas, although it’s probably too late to put drywall on the inside. Once I run speaker wires it’s ready for insulation. The plan is dense pack cellulose for insulation – approximately 6” thick. I considered mineral wool because I can do it myself but I think the dense pack cellulose might give better results. I’d like to make it as well thought out and legit as possible. DIY and not spending piles of money though.

I'm open to any suggestions, thanks!
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Re: Under Garage Home Theater Build

#30 Post by Bill Fitzmaurice »

If you insulate it's for the usual reason, to keep it warmer in winter, cooler in summer. My basement is the same, a poured concrete foundation and floor. It was bare when I moved in, I framed it with steel studs, insulated with fiberglass, sheathed with drywall. Some of the foundation is above ground, by as much as two feet, so I dug a trench a foot deep around the foundation and put two inches of urethane foam board on the foundation from the bottom of the trench to the top of the concrete. I coated that with sprayed on white Duratex that I'd tinted gray, so it looks like concrete.

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